The present invention related to fluid pressure operated actuators and more particularly to a fluid pressure actuator and locking means for locking the actuator in the extended position, which may be utilized in the landing gear structure of aircraft or for any other application where it is desired to utilize fluid pressure activated means for moving an element to an extended position and for thereafter locking the element in such position.
Heretofore, numerous types of fluid pressure actuators incorporating locking means have been proposed and utilized, particularly in connection with the aircraft industry, and while these prior art devices have operated satisfactorily insofar as providing a motive force for moving an element from one position to another, the locking means incorporated therein have not been entirely satisfactory.
Some prior art locking means have involved relatively delicate toggle mechanisms, with consequent liability to failures, and have been relatively complex and costly to manufacture and repair. Also, in some instances, as the result of wear, play has developed between the parts of the locking mechanism, which has sometimes resulted in failure to provide a positive lock with the result that inadvertent movement of the element operated by the fluid pressure actuator has taken place, which in certain instances could be disastrous.
Other prior art locking means involve rollers secured within recesses of plungers, the rollers operating against camming surfaces to operate locking detents, but those proposed require sliding action of the rollers under the high radial loads induced in the detents. One such prior art device is the subject of U.S. Pat. No. 3,107,582 to Royster. Referring to FIG. 2 of this patent, the detents 65 are loaded in the direction shown by the arrow due to the load applied against the detent by the level surface 66. Retraction of the plunger 58 in the direction shown by the arrow is necessary to release the lock. While rolling action between the roller 74 and the detent cam surface 67 is obtained, sliding action is required between the rollers and their recess 70. It is characteristic of sliding friction that the magnitude of the friction is proportional to the loading normal to the surfaces. Furthermore, the exact value of the coefficient of friction varies considerably with the production pieces. These characteristics, in combination, result in large variations in the force necessary to move the plunger. This, in turn, introduces a large spread between the hydraulic pressure below which the actuator cannot unlock and that above which it will always unlock. A further disadvantage of the sliding friction is the tendency for high axial loads on the plunger should a detent become "sticky" in the locking-mode. This axial force can overcome the force applied by the plunger spring and prevent the detents from locking.
An actuator which locks in the retracted position is known which is generally similar to that of Royster U.S. Pat. No. 3,107,582 except that a cage is provided at the outer end of a locking piston and the rollers are held in alignment normal to the center line of the actuator by the cage but are unrestrained radially by the cage or locking piston.